That link takes me to a login page that when I log in showns me something presuambly different to what you see.

I get one option in a drop down "free software" which then shows JBoss Eclipse thingy and Portal.

The dropdown list should show you all the platforms for which your company has an entitlement. If this is not correct then you should raise a supoprt ticket and have it fixed.

Is SOA-P open source?

The SOA platform consists of a number of open source projects which have been integrated, QE'd and released as a single artifact. A single source bundle for all the integrated projects is provided from the earlier link.

The source for each of the individual projects is also available through their communities, for example JBoss ESB is a core project within the SOA platform and its source is located in the following repository http://anonsvn.jboss.org/repos/labs/labs/jbossesb/.